1. Field of the Invention
The present invention relates to a fusion splicing method and a fusion splicer for different-diameter optical fibers, in which optical fibers with different diameters are heated by arc discharge, laser irradiation, and the like for fusion splicing.
2. Description of the Related Art
In some cases, optical fibers with different diameters are connected to each other. For example, optical fibers with outer diameters of 125 μm and 400 μm are connected. This optical fiber with an outer diameter of 400 μm often has a short length of about 2000 μm. Such a large-diameter and short-length optical fiber is not used as a normal optical transmission path but used as a optical device such as a collimator. Therefore, the term “optical fiber” may not be proper for such a material, but the material has a shape and a structure of an optical fiber. In the light of the shape and structure thereof, the term “optical fiber” is used in this application even if it is the optical device.
First, a description will be given of a conventional method of fusion splicing optical fibers with the same diameter. As shown in FIG. 3A optical fibers 21 and 22 are first aligned in X and Y directions such that central axes thereof coincide with each other and ends of the optical fibers 21 and 22 are spaced apart (for example, several hundreds μm). The X and Y directions are directions perpendicular to each other in a plane perpendicular to a Z direction (for example, horizontal and vertical directions in FIG. 3A), the Z direction being a direction of the axes of the optical fibers 21 and 22. Next, after completion of the alignment in the X and Y directions, the ends of the both optical fibers 21 and 22 are brought close to each other symmetrically with respect to a heating region 30 as shown in FIG. 3B, and the interval therebetween is maintained at, for example, about 10 to 20 μm. Preheating for a certain period of time (for example, several hundreds msec) is then performed. Without this preheating, the ends of the both optical fibers 21 and 22 remain hard, which tends to cause misalignment of the axes when end surfaces advance into contact with each other.
When the both end faces are softened, the optical fiber 21 on one side (for example, left side) is advanced, and the end face of the optical fiber 21 is brought into pressure-contact with the end face of the other optical fiber 22 as shown in FIG. 3C. Then, main heating performed for several seconds. Accordingly, the both end faces are fused and bonded to each other, thus achieving connection with low connection loss.
Fusion splicing different-diameter optical fibers is disclosed in the Japanese Patent Laid-Open publication No. 2003-21745. Preheating and main heating with the ends of the both optical fibers is performed while they are located at asymmetric positions with respect to the heating region, that is, with the ends of the both optical fibers asymmetrically located with respect to the center of the heating region.
Specifically, as shown in FIG. 4, the preheating is performed while the end of an optical fiber 11 with a small diameter is retracted from the center of a heating region 30 and the end of an optical fiber 12 with a large diameter is advanced to the vicinity of the center of the heating region 30. Subsequently, one of the optical fibers 11 and 12 is advanced, and the main heating is then performed with the optical fibers 11 and 12 brought into contact with each other.
The above described preheating with the ends of the both optical fibers 11 and 12 asymmetrically located with respect to the heating region 30 is for unequalizing amounts of heat to be applied to the both optical fibers 11 and 12. If positions of the ends of the optical fibers 11 and 12 with different diameters are symmetrically located with respect to the heating region 30 as in the case of the aforementioned optical fibers 21 and 22 with a same diameter, the amounts of heat to be applied to the optical fibers 11 and 12 are equalized.
Accordingly, the softening states of the both optical fibers due to the preheating are different from each other because the optical fibers 11 and 12 have different heat capacities according to the different diameters. For example, when an amount of heat proper suitable for the small-diameter optical fiber 11 is applied thereto, the end face of the large diameter optical fiber 12 remains hard because the amount of heat applied thereto is insufficient.
On the other hand, if the large diameter optical fiber 12 is applied with an amount of heat proper suitable therefor, an excessive amount of heat is applied to the small diameter optical fiber 11, and the end face thereof is excessively softened and increasingly fused. Accordingly, the end portion thereof changes in shape and in the extreme case becomes a spherical shape due to surface tension. However, if the amounts of heat to be applied to the both optical fibers 11 and 12 in the preheating are unequalized by performing the preheating while the positions of the ends of the optical fibers 11 and 12 with different diameters are arranged symmetrically with respect to the heating region 30 as described above, the respective optical fibers receive proper amounts of heat, thus such a disadvantage being eliminated.
Such unequalized heating is also described in the following Publications. The Japanese Patent No. 2958060 discloses a method of fusion splicing an optical fiber and a glass optical waveguide by carbon dioxide laser irradiation with the end faces thereof abutting on each other. In the method, a beam spot of the irradiated carbon dioxide laser beam is an ellipse, and an irradiation region on the glass waveguide side is made larger than that on the optical fiber side.
Thus, a larger amount of heat is applied to the glass optical waveguide, which has a larger heat capacity, than the optical fiber. In the Japanese Patent Laid-Open publication No. 5-72439, an end face of a waveguide and an end face of an optical fiber are fusion spliced by irradiation of an arc biased to the side of the end face of the waveguide. The arc is biased by biasing arc discharge with a magnetic field. The Japanese Patent Laid-Open publication No. 11-287922 discloses a case where a quartz optical fiber and a non-quartz optical fiber are heated by arc discharge or laser beam irradiation for fusion splicing. In this case, only the non-quarts optical fiber is heated while a distance between the end faces of the both optical fibers is maintained at 0 to 20 μm, thereby only the non-quarts optical fiber is softened and fused to be fusion-spliced to the quartz optical fiber.
However, all the conventional arts disclosed in the above Publications implement the unequalized heating by adjusting the spatial relationship between the heating region and a position in which end faces of the both optical fibers abut on each other. Accordingly, the conventional arts have low degrees of freedom of the adjustment, and cases to which the conventional arts can be applied are limited. Specifically, in the case of fusion splicing optical fibers with different diameters, the difference between the heat capacities thereof varies, and it is required to adjust the unequality of the amounts of heat to be applied thereto according to the difference. However, it is not easy to freely adjust the unequality of the amounts of heat to be applied only by adjusting the spatial relationship.
The present invention has been made in the light of the aforementioned problem. And an object thereof is thus to provide a fusion splicing method and a fusion splicer for optical fibers with different diameters, which are improved so as to facilitate proper adjustment of unequality of amounts of heat to be applied to end faces of optical fibers with different diameters by controlling amounts of heat applied thereto in terms of time and thus easily perform optimal fusion splicing of the different-diameter optical fibers.